Update MSG_BACK c=18

Firmware/messages.c

@@ -61,7 +61,7 @@ const char MSG_EJECT_FILAMENT[] PROGMEM_I1 = ISTR("Eject filament"); //// Number
 const char MSG_CUT_FILAMENT[] PROGMEM_I1 = ISTR("Cut filament"); //// Number 1 to 5 is added behind text e.g. "Cut filament 1" c=16
 const char MSG_M117_V2_CALIBRATION[] PROGMEM_I1 = ISTR("M117 First layer cal."); ////c=25
 const char MSG_MAIN[] PROGMEM_I1 = ISTR("Main"); ////c=18
-const char MSG_BACK[] PROGMEM_I1 = ISTR("Back"); ////
+const char MSG_BACK[] PROGMEM_I1 = ISTR("Back"); ////c=18
 const char MSG_SHEET[] PROGMEM_I1 = ISTR("Sheet"); ////c=10
 const char MSG_STEEL_SHEETS[] PROGMEM_I1 = ISTR("Steel sheets"); ////c=18
 const char MSG_MEASURE_BED_REFERENCE_HEIGHT_LINE1[] PROGMEM_I1 = ISTR("Measuring reference height of calibration point"); ////c=60